This is a continuation of International Application PCT/EP00/07793, filed on Aug. 10, 2000, which was published in German under PCT Article 21(2), the contents of which are incorporated herein by this reference.
Pattern adapters for circuit board tester are used to convert a predetermined regular grid pattern of a tester into the usually irregular test point arrangement of a circuit board to be tested. The pattern adapter comprises, as a rule, several guide boards spaced away from each other including guide holes for receiving test needles. The test needles are arranged canted in the adapter so that they can electrically connect the contact points of the regular grid pattern to the circuit board test points since these, as a rule, deviate from the regular arrangement of the grid pattern.
The spacing of test points on the circuit boards is constantly decreasing. Currently, the spacing is a mere 0.3 mm (12 mil) or 0.25 mm (10 mil), for example. The test needles at the side of the adapter facing the test object need to be arranged on a correspondingly tight pitch.
This is why extremely thin test needles are used for such adapters. The test needles have a diameter of 0.1 mm or 0.2 mm, for example. These test needles are extremely delicate or unstable so that many guide boards are needed in the adapter to reliably ensure good guidance.
Also known are test needles that have differing diameters along their length with steplike transitions between individual portions of the needles. The portion of the test needle at the contact tip, which is to be contacted to a test point of the circuit board to be tested, has the smallest diameter. The needle""s diameter then increases stepwise with increasing distance away from the contact tip. As compared to thin, constant-diameter test needles, these stepped test needles are substantially stiffer and can also be arranged with their contact tips located relatively close to each other. Nonetheless, the portion adjoining the contact tip is also very delicate or unstable so that it needs to be supported in the pattern adapter by several test boards.
German Utility Model DE 91 00 432 U1 concerns a test needle for an electric test adapter. The test needle is conically pointed at the free end, the tip comprising a spherical rounding with a radius of approx. 50 xcexcm. This German Utility Model teaches that the radius of the spherical tip should be in the range of 20 to 80 xcexcm.
German Utility Model DE 298 10 384 U1 concerns conically-pointed test needles with no indication of test needle thickness.
DE 37 36 689 A1 and DE 36 39 360 A1 describe probes having a conically pointed tip and a spherical head at the end remote from the test tip. The largest shank diameter of these needles is in the range of 1.3 to 1.4 mm and the diameter of the head is approx. 2 mm. No indication is given as to the diameter of the contact tip.
Probes are evident from DE 44 17 811 A1, which feature a very short conical tip for contacting a contact point.
DE 44 39 758 A1 discloses a probe for a test adapter, which again features a short and conical tip. The tip is produced by grinding. This reference citation shows an adapter including test needles arranged canted in part.
DE 36 20 947 A1 shows a test needle consisting of a constant cross-section wire, the diameter of which is less than 0.2 mm. Also shown is a further pointed test needle.
A pointed test needle is illustrated in U.S. Pat. No. 4,403,822 with no indication as to the thickness of this test needle.
DE 44 39 758 C2 describes probes made of a thin wire, which is 0.15 mm to 0.5 mm thick. These probes have a short tip.
DE 196 54 404 A1 proposed a complicated solution for testing circuit boards on a pitch spacing of 200 xcexcm, in which an adapter including test needles is used to contact the contact points on a very tight pitch by means of a translator foil. This application makes it clear that there is no direct solution to contacting contact points on a tight pitch.
The use of smooth non-contoured music wire probes in an adapter is proposed in DE 43 23 276 A1. In this adapter a solid material body is penetrated by test needle passageways, in which the thin test needles are reliably guided. These test needles may have a diameter of up to 0.1 mm.
German Utility Model DE 296 16 272 U1 discloses an adapter having an internal adjustment mechanism.
The present invention concerns a test needle for a pattern adapter of a circuit board tester, which can be optimally configured so that it is highly stable and can achieve a tight pitch between the test tips of two adjacent test needles in a pattern adapter.
In general according to one aspect, the invention features a test needle for a pattern adapter of a circuit board tester. The test needle comprises a contact portion for contacting a circuit board test point, which portion is configured with a conical taper to a free contact tip. The contact portion has a length of at least 15 mm and at the contact tip a diameter smaller than 0.2 mm. An end section of the contact portion opposite the contact tip is in the range of 0.3 mm to 0.4 mm.
The contact portion, which is conically tapered to the contact tip, represents an optimum trade-off between very thin test needles suitable for contacting circuit board test points on a very tight pitch and thicker test needles having enhanced stability and thus are easier to guide in a pattern adapter, i.e. require fewer guide boards.
Since the cross-section of the test needle in accordance with the invention is widened in the portion before the contact tip, the contact portion is substantially stiffer than test needles having a contact tip where the diameter is the same as the diameter in the contact portion. This applies also in comparing stepped test needles as described above. The thinnest section of these stepped test needles comprises the contact tip, which is substantially more flexible than the contact portion of the test needle in accordance with the invention for the same diameter at the contact tip. It has been discovered that in an adapter having test needles in accordance with the invention the guide board, which is needed with an adapter having stepped test needles, can be eliminated.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.